Fiber production is realized by heating and drawing polyester (such as polyethylene terephthalate, polyethylene naphthalate and polylactic acid) and polyamide (polyamide 6, polyamide 66) thermoplastics. During fiber production, heat treatment which is applied in order to draw fiber material in yarn form is generally performed via heated rollers and chambers along the line. In heated chambers used in heating the material used in fiber production, hot air or vapor application is performed. In this way, yarn is annealed and the given form is enabled to be preserved. For heating, conventional methods, infrared beams and vapor are currently preferred. Heat treatment allows plasticization and drawing of the fiber material by means of heat in fiber production process. Furthermore, heat treatments applied for the crystallization of fiber by annealing at a temperature close to crystallization are provided via the abovementioned methods.
The thermal conductivity of polymers used in fiber production, for example polyester (polyethylene terephthalate, polyethylene naphthalate, polilactic acid etc.), polyamide (polyamide 6, polyamide 66 etc.) is low. For this reason, heat is not distributed homogenously along fiber during heat treatment. The distance to the heat source during process can prevent the heat from reaching regularly and continuously to the fiber and can cause the surface and inside of the fiber to cool differently (to form “skin-core” structure).